In general, to a sheet material such as textile fabric, the cutting is performed to cut it based on a pattern paper or on the data corresponding to the pattern paper. A cutting machine or the like used for the cutting has a grinding function to keep sharpness of a cutting blade (Cf. Patent Citation 1, for example). The Patent Citation 1 discloses a sheet material cutting device for cutting the sheet material with a cutting knife which is moved in reciprocation along a vertical axial line direction and also discloses two different ways of grinding the cutting knife from both sides of its cutting edge.
FIG. 15 shows those two different concepts on the grinding disclosed by Patent Citation 1. FIG. 15(a) shows one concept on the grinding with a rounded surface around outside of periphery of a rotary whetstone disclosed in FIG. 11 and the like. FIG. 15(b) shows another concept on grinding with a flat surface of the rotary whetstone. The flat surface is perpendicular to the axis of the rotary whetstone, as disclosed in FIG. 13 and the like of the Patent citation 1. In the following, the simplified construction is illustrated, for explanatory convenience. Although names and reference numerals of parts may vary, the correspondence relation to the two different concepts on the grinding should be obvious.
In FIG. 15(a), one side 1b of the cutting edge 1a of the cutting knife 1 and the other side 1c of the same are ground with outside surfaces 2a, 3a of outer peripheries of two rotary whetstones 2, 3, respectively. The two rotary whetstones 2, 3 are supported at front ends of two arms 4a, 4b of a support block 4. The two arms 4a, 4b are fixed with spaced apart from each other at a certain angle. The support block 4 is capable of oscillating displacement around a pivot shaft 5 penetrating intermediate portion between the arms 4a, 4b. The pivot shaft 5 supports the cutting knife 1 so as to be capable of moving in reciprocation along a direction vertical to the paper, and is stuck up from base 6 which turns in conjunction with a direction of the cutting edge 1a of the cutting knife 1. When the support block 4 is made oscillating displacement with respect to the pivot shaft 5 in one direction or the other, the one side 1b of the cutting knife 1 or the other side 1c of the same can be ground with the related outside surface 2a, 3a of the rotary whetstone 2, 3. In this regard, however, since the grinding is performed using the cylindrical surface 2a, 3a, even when one side 1b and the other side 1c of the knife 1 initially have a linear cross-sectional shape, they are varied in cross-section to have a concave surface, as shown as a shaded area.
In FIG. 15(b), like reference numerals are labeled to corresponding parts to FIG. 15(a), to avoid redundant explanation. The support block 4 has mounting surfaces 4c,4d on the arms 4a,4b at the side facing to the cutting edge 1a of the cutting knife 1 respectively. The rotary whetstones 2, 3 have rotate shafts perpendicular to the mounting surfaces 4c,4d and are capable of changing over between grinding states, in which flat surfaces 2b,3b perpendicular to the rotate shafts are put in contact with the one side 1b of the cutting knife 1 or the other side 1c of the same to grind it. For example, when the support block 4 is pivotally displaced in one direction with respect to the pivot shaft 5, as showing with the dashed line, the flat surface 2b of the rotary whetstone 2 is switched over to the state of being put in contact with the one side 1b of the cutting knife 1 to grind it. Likewise, when the support block 4 is pivotally displaced in the other direction with respect to the pivot shaft 5, the flat surface 3b of the rotary whetstone 3 is switched over to the state of being put in contact with the other side 1c of the cutting knife 1 to grind it. As the cutting knife 1 is ground with the flat surfaces 2b, 3b, the linear cross-sectional shape of the cutting knife 1 is kept unchanged, as shown as the shaded area.
Such grinding way of FIG. 15(a), is not only possible by an overall oscillation displacement of the support block 4, but also possible by putting the cylindrical surfaces 2a, 2b of the rotary whetstones 2, 3 in contact with the one side 1b of the cutting edge 1a of the cutting knife 1 or the other side 1c of the same, respectively, via a link mechanism and the like (Cf. Patent Citation 2, for example). According to Patent Citation 2, the rotary whetstones 2, 3 and the whetstone supporting structure are contained in the turning cylinder which is turned around an R-axis as a rotation shaft of the cutting edge of the cutting blade corresponding to the cutting knife 1. The switching over between the grinding states is performed by turning the turning cylinder while locking a slide ring mounted on the turning cylinder to be stationary relative to outside. By a relative angular displacement between the slide ring and the turning cylinder, each rotary whetstone pivotally displaces individually via the cams and the link mechanism, thereby allowing the switching over between the grinding states.    Patent Citation 1: JP Patent Publication No. Sho 56-8759    Patent Citation 2: JP Patent No. 3390219